Initial reports put the cost of the military equipment sale, which include Bell Boeing V-22 transport helicopters, at $10 billion; Hagel's 5-day Middle East visit is expected to focus on Iran, the Syrian civil war and weapons sales to America's allies Israel, Saudi Arabia, and the United Arab Emirates.

U.S. Defense Secretary Chuck Hagel on Monday met Israeli Defense Minister Moshe Ya'alon and finalized the sale of an undisclosed number of Bell Boeing V-22 transport helicopters and other U.S. military equipment including Boeing KC-135 inflight refueling planes, advanced radar systems for fighter planes and anti-radiation missiles at a reported cost of $10 billion dollars.

Hagel and Ya'alon announced the sale during a joint press conference in Tel Aviv. The U.S. defense secretary said the new military equipment was intended to "ensure Israeli air superiority" for years to come, and prefaced the sale by saying Sunday that the deal should send a clear message to Iran.

"Today we took another significant step in the U.S.-Israel defense relationship," Hagel said, reiterating Washington's "iron-clad pledge" to ensure Israel's qualitative military edge in a region rocked by turmoil.

"Minister Ya'alon and I agreed that the United States will make available to Israel a set of advanced new military capabilities ... including anti-radiation missiles and advanced radars for fighter jets, KC135 refueling aircraft, and most significantly the V-22 Osprey, which the United States has not released to any other nation."

Ya'alon told reporters at the start of the press conference that the arms sale clearly indicated the Washington's support of and commitment to Israel.

"The United States and Israel are contenting with the challenges in this tough neighborhood of ours, first and foremost Iran," Ya'alon said. "Our countries' commitments to one another is being expressed in the American support for Israeli security. We see this commitment in the Iron Dome, which has saved lives, and we see this commitment also in the presidential approval of deal, including now, with the V-22.

The Israeli defense minister also asked his American counterpart to send his condolences to the victims of the Boston Marathon bombings.

At the news conference with Ya'alon, Hagel was asked whether he believes it would be advisable for Israel to attack Iran on its own.

"That calculation has to be made by" Israel, he replied after noting, "Israel is a sovereign nation; every sovereign nation has a right to defend itself."

Hagel did not mention a concern that U.S. officials have voiced in the past, namely, that an Israeli strike would run the risk of igniting a wider war that could draw in the United States.

Ya'alon was asked about reports that the Syrian government has used chemical weapons in its struggle against rebel forces.

He did not specifically say whether Israel believes such weapons have been used, but he said that Syria must not cross the "red line" of allowing any chemical weapons to fall into the hands of what Ya'alon called "rogue elements."

He said that "red line" has not yet been crossed.

Hagel kicked off a week-long, five-country regional visit Sunday, a trip which expected to focused on Iran, the Syrian civil war and weapons sales to America's allies Israel, Saudi Arabia, and the United Arab Emirates.

Hagel is using his first visit to Israel as Pentagon chief to underscore his view that Israel must decide for itself whether and when to use military force against Iran. He told reporters on his flight from Washington that Israel has every right to defend itself, and that Israel and the U.S.­ share the objective of preventing Iran from acquiring a nuclear weapon.

"Israel will make the decision that Israel must make to protect itself, to defend itself," Hagel told reporters during the flight. He said there is "no daylight at all" between Israel and the U.S. on the central goal of preventing a nuclear-armed Iran, but added that there "may well be some differences" between the two allies on the question of when Iran's leaders might decide to go for a bomb.

But he added, "When you back down into the specifics of the timing of when and if Iran decides to pursue a nuclear weapon, there may well be some differences."

Israeli officials say the arms deal aims in part to preserve Israel's military superiority in light of weapons contracts with other countries in the region.

The U.S. Defense Department has called Hagel's visit a continuation of contacts following President Barack Obama's trip here last month. The Iranian nuclear issue will be front and center in Hagel's defense-related meetings, along with the changing situation in Syria. On Monday, an honor guard will be on hand at Tel Aviv's Kirya army base to honor Hagel.

From Israel, the defense secretary will travel to Amman to discuss the implications of Syria's civil war on Jordan, before proceeding on to Saudi Arabia, Egypt and the United Arab Emirates. In the UAE Hagel is expected to move to finalize the sale of 25 F-16 fighter planes. The deal is set to include training in the United States of UAE combat pilots.